It's going to be difficult, but I'll wager that in the long term, as we learn more about the devastating long-term effects of concussions, there will be no reasonable alternative. Rugby already has them, and they don't seem to have a major problem with abuse, so I think it can be done. The key part of making it work is convincing everyone that it really does matter for player health, so that everyone takes it seriously. Follow the science.
I joke about it, but there is no question he will tear up the league - his previous record is frightening and I can't believe he'll suddenly turn into a donkey just because he's playing in England. Unless he picks up a long-term injury he'll score between 0.5-1 goals per game on average, so potentially something like 50+ including cups and Europe. Totally insane.
If the club are serious about giving ten Hag time and resource to turn things round, this season is a writeoff. He can't be expected to right the ship much at all at this point because, as you alluded to, he is probably thinking he is a handful of transfer windows away from having the squad he thinks he needs.
Richest club, most resources. Every season they don't win the title is a significant failure given that they have an advantage over every other team in the division. Ditto the Champions League (which is why their perennial failure there is so massively heartwarming for everyone else).
They'll have their usual little slump every year but the tiny handful of points they'll drop won't be enough for Liverpool to catch them. (I'd love to be wrong of course).